Making electronic circuits including a band-gap stage to provide a reference voltage is generally well known. This reference voltage must, in principle, be regulated to be independent of temperature.
As shown in FIG. 1, this type of band-gap electronic circuit 1 is formed of a diode, such as a bipolar transistor N1 in a diode arrangement traversed by a continuous current Ic generated by a current source Sc to define a diode voltage VBE. Generally, this diode voltage VBE decreases with an increase in temperature, and conversely increases with a decrease in temperature. Current source Sc and the diode-connected bipolar transistor N1 are series-connected between two terminals of a continuous supply voltage.
Since diode voltage VBE varies inversely with temperature variation, there is also provided a generator 2 of a voltage K·UT, wherein voltage K·UT varies inversely with diode voltage VBE. This voltage K·UT is added in an adder 3 to the diode voltage to supply a reference voltage VREF, which is equal to VBE+K·UT. Factor K is thus adapted to obtain a reference voltage VREF which is independent of temperature. To achieve this, dVBE/dT must be equal to −K·dUT/dT. Reference voltage VREF, which may be a band-gap voltage, has a value substantially equal to 1.22 volts at 0° C. The thermodynamic voltage UT, which is equal to k·T/q, has a value of around 23.5 mV at 0° C., where k is the Boltzmann constant, T is the Kelvin temperature and q is the charge of an electron in absolute value.
Generally, for the type of band-gap electronic circuit shown in FIG. 1, a default value of factor K is set when the electronic circuit is designed in order to have a temperature-independent reference voltage VREF. This factor K affects the absolute reference voltage and first order temperature dependence. During adjustment of the absolute value of the reference voltage, the factor K variation also affects temperature stability. Since the method for manufacturing this type of electronic circuit may vary for adjusting the reference voltage, this may result in non-optimum temperature stability. This leads to variation from one electronic circuit to another with a reference voltage that is not entirely temperature-independent, which is a drawback.
US Patent Application No. 2006/0043957 A1, which discloses an electronic circuit of this type, provided with a band-gap stage, may be cited in this regard. This Patent Application discloses a way of adjusting the temperature coefficient. To achieve this, voltage measurements are taken at different temperatures in order to calculate the slope and thus adjust the reference voltage generated. This band-gap stage therefore supplies a precise reference voltage following different temperature coefficient adjustment measurements. However, the adjustment method requires several measuring steps in order to extract the precise reference voltage adjustment parameters, which is a drawback. Moreover, the reference voltage adjustment is highly dependent on variations in the electronic circuit manufacturing parameters, which is another drawback.